long span piping-pipe on supports

8/13/2019 Long Span Piping-pipe on Supports

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Shown below are sketches of three cases of long-span or pipe-on-supports situa-tions. Case #1 shows traditional pipe-on-supports installations where one support isprovided for each length of pipe. Cases #2 and #3 show long-span pipe assemblies thatutilize AMERICANs Toruseal gaskets. Other pipe assemblies using other AMERICANjoints may be possible depending upon circumstances. Notes under each case apply tothat case. General notes are shown at the end.

LONG SPAN AND PIPING SUPPORTS

*Check AMERICAN on long-span requirements involving 4 pipe.**See Sections 6 and 8 for details on Toruseal Gaskets.

Approx. 20' Max.

(Typ.)

Approx. 2' (Typ.)

Case #1

Case #1 utilizes 20' or less lengths of Fastite, MJ, or other push-on restrained pipe.(See page 7-29 General Note 3.) This length is normally subject to normal manufactur-ing and trim (cut pipe) variations, with some pipe allowed up to two feet shorter thanfull length. Where exact length pipe is required, say to fit existing pier spacings, etc.,check AMERICAN.

Minimum pressure classes of all sizes of ductile iron pipe are more than adequateto support the weight of the pipe and the water it contains in Case #1 installationswhen analyzed and installed in accordance with the suggestions in the Ductile Iron PipeResearch Associations procedure for Design for Ductile Iron Pipe on Supports. Thisprocedure is available from AMERICAN.

The beam strength of ductile iron pipe, along with the capability of certain AMERI-CAN joints, allows the installation of clear spans of up to 48' or more in sizes 6* - 64.This was made possible due to the advent of AMERICANs unique Toruseal gaskets**in the 1970s.


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APPROX. 48' - 0" STD.

APPROX. 2' - 0" STD.

9' - 6"19' - 3" (TYP.) 19' - 3" (TYP.)

Case #3

Case #3 utilizes 19-3 lengths of flange-bell and flange-plain end pipe with a 9-6 flange-flange pipe in the center. This can result in more mid-span deflection thanCase #2 and, therefore, it is normally used only in 18 and larger sizes.

The 48 clear span distance for Case #3 has been increased in larger pipe size appli-cations by lengthening the 9-6-long center pipe (maximum possible with three full-length pipes is 58-6). Check AMERICAN on requirements greater than 48 or forlonger desired spans in smaller pipe sizes than is illustrated in Case #2.

Since Case #3 utilizes flanged pipe joints, minimum nominal thicknesses for fabri-cated flanged pipe shown in AWWA C115 are required.

Approx. 38'-6" Std.

Approx. 2' (Typ.)

Case #2

Case #2 utilizes 19-3 lengths of flange-plain end and flange-bell (Fastite, MJ, orother push-on restrained) pipe. (MJ pipe is not available over 12 in diameter.) SinceCase #2 utilizes flanged pipe joints, minimum nominal thicknesses shown in AWWAC115 are required.


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GENERAL NOTES

1. Principles presented in the DIPRA publication Design of Ductile Iron Pipeon Supports can be used to calculate the maximum localized stress due to supportreaction and to approximate the maximum beam-bending stress near mid-span ofthese systems. This publication can be obtained from AMERICAN.

2. Small-diameter pipe systems with very long unsupported pipe spans canexhibit visible mid-span deflection, or sag. While this deflection results in nostructural problems, the designer may consider means to reduce or eliminate mid-span deflection if aesthetic or other concerns are anticipated in the application.

3. Push-on or push-on restrained joint pipe is normally a better choice thanmechanical joint pipe due to more tolerance for thermal expansion and contraction,movement effects, and other aspects. Mechanical joints are not available fromAMERICAN for ductile iron pipe over 12.

4. Where pipeline bends adjacent to crossings are externally restrained forrestraint of axial pressure thrust, or where there are no bends adjacent to crossingsto result in such thrusts, it is quite common to install push-on or mechanical pipejoints with a slight axial gap (1/8-1/4) between the spigot and the back of thesocket, and with the pipe sections firmly strapped to shaped pier supports locatedimmediately behind the pipe bells as indicated. This is appropriate for normal antici-pated thermal expansion and contraction of individual pipe sections and is easy toaccomplish in the field by assembling the joints to metal contact condition and thenbacking them out slightly. Slight rebating deflection (or wiggling) of the jointcan produce the desired results, with field marking of the relative position of thespigot to the bell face to gauge results.

5. It is generally recommended that effective lateral restraint (means of assur-ing lateral stability of joints) be provided for the joints of all pipe-on-support installa-tions, particularly in pressure pipelines and in other cases where lateral or columnarforces may exist to deflect joints or to dislodge the pipeline from the supports.Unstabilized, single rod or other hangers may not be desirable for pressure or otherpipelines.

6. Contact AMERICAN where other design factors are a consideration. Systemswhere crossing pipe is subject to axial thrust forces or movements from bends, etc.,long bridge crossings, large or concentrated thermal expansion-contraction effects,pipe-on-rollers, etc., are applications that may involve special design concerns.

7. The piping layouts as per Cases 2-3 consider the possibility of projects withsizable numbers of exact length repetitive pipe spans. Where lesser numbers of

spans are involved on candidate projects, it may be practical and more economicalto provide slightly longer standard spans, say by furnishing longer laying lengthintermediate flanged pipe (see Sec. 8) in lieu of the 19'-3" lengths depicted in thesecases, etc. Contact AMERICAN if this is necessary or desirable.

long span piping-pipe on supports

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